Preterm birth is the most important problem in obstetrics, because it occurs commonly and is associated with neonatal mortality as well as morbidity in survivors. Despite extensive research, little progress has been made in decreasing the rate of preterm birth, largely due to our general lack of understanding of the underlying pathophysiology. Epidemiological studies have identified numerous risk factors for preterm birth, especially a history of a prior spontaneous preterm birth and mid-trimester cervical shortening. Cervical shortening less than 25 mm (10th percentile) diagnosed by transvaginal ultrasonography in the mid-trimester is one of the most powerful markers of recurrent preterm birth in women with a history of a spontaneous preterm birth, and cervical cerclage has become a widely utilized effective intervention in these women. Nevertheless, not all women who undergo an ultrasound-indicated cerclage will subsequently deliver a term infant. There remains an incomplete understanding of the pathophysiologic mechanisms and pathways underlying the initiation of preterm birth, especially in regard to the pathway that includes asymptomatic cervical shortening. The contribution of inflammation to the spontaneous preterm birth syndrome is well- established, but less is known about the association between inflammation and cervical shortening. While prior studies have focused on a systemic inflammatory response, recent interest has shifted towards defining a potential set of biomarkers that could define characteristics of a more localized response. In this grant application, we propose to measure concentrations of inflammatory mediators and markers of collagen remodeling in a well-characterized cohort of high-risk women who have had a prior spontaneous preterm birth between 17 0/7 and 33 6/7 weeks' gestation. We will evaluate: 1.) whether cervicovaginal fluid analyte concentrations differ in women who develop cervical shortening (<25mm) compared to those women who maintain a cervical length (=25mm). 2.) In high-risk women who develop mid-trimester cervical shortening (<25mm), to evaluate: a) Whether cervicovaginal fluid analyte concentrations measured at the time that cervical shortening is recognized can identify women in whom cerclage confers the greatest benefit, or alternatively harm. b) Whether the change in cervicovaginal fluid analyte concentrations between the baseline measurement and the measurement at the diagnosis of cervical shortening can predict response to cerclage and subsequent pregnancy outcome. Realizing these aims will not only lead to a better understanding of the spontaneous preterm birth syndrome, but will also help clinicians define more individualized and effective strategies for managing women with cervical shortening who are at high risk for recurrent preterm birth. This information will also assist investigators in identifying which women are at the highest risk for recurrent preterm birth and who may be good candidates for future intervention trials of alternate therapies.